Well, it's clearly the Starfleet insignia. The point is that they were trapped on the planet with no communications and needed to be beamed up before an ion storm hit or some bullshit, and that big symbol in the sand made of human footprints was apparently supposed to be their signal to a ship in fucking space to help locate them. If they could detect a fucking pattern of footprints, they could detect the goddamn lifeforms walking them.
That's my real issue. It was done for a cheap gag/hype moment, but it completely threw all logic out the fucking window for the sake of it. Star Trek plots aren't always completely bulletproof, but this wasn't even fucking trying to be. At least when they played Sabotage in Beyond, they had a technobabble reason for it.